Forming balls from powder



United States Patent 3,368,004 FORMENG BALLS FROM PGWDER AurelioFrederick Sirianni and Ira Edwin Puddington,

Ottawa, Ontario, Canada, assignors to Canadian Patents and DevelopmentLimited, Ottawa, Ontario, Qanada, a

corporation of Canada No Drawing. Filed ()ct. 21, 1965, Ser. No. 500,223

17 Claims. ((31. 264.5)

ABSTRACT OF THE DISCLOSURE Powders are formed into balls or spheres in atwophase liquid, the first liquid being inert and the second having apreferential affinity for the powder, by shaking the three-phase systemin a container having rounded surfaces to agglomerate the powder andsecond liquid and cause the agglomerates to undergo impact andricocheting action until the balls are shaped and densified, and thedesired balls subsequently recovered from the system.

This invention relates to the production of balls from powderedmaterials. A process is described by which finely divided metallic orsinterable material can be formed into balls, spheres or similar roundedshapes simply and economically. In particular, a process is describedfor forming balls or spheres of accurately controlled size, sizedistribution, and shape in a two-phase liquid system.

In the past metallic balls have been prepared by molding and machiningoperations (such as casting, pressing, or extruding-and-cutting),followed by finishing operations (e.g., final shaping by rolling orgrinding, and polishing). These conventional operations are notsatisfactory when applied to metallic materials of high melting pointand hardness. These latter materials are usually formed by powdermetallurgy techniques including compacting in dies, sintering,machining, and surface finishing. Due to their molding properties somepolymeric materials such as polytetrafiuoroethyleue are usually formedby similar techniques. In these prior art techniques costly molds ordies having a limited life and production rate are usually required forthe initial shaping. The formation of rough pellets from powders by drytumbling in a drum, is also known.

An object of the present invention is to provide balls, spheres, orother round shapes of controlled size and shape without the use ofexpensive dies or molds. Another object is to provide a process forforming large numbers of accurately shaped balls from sinterablepowdered material in a simple manner. A further object is to provide aprocess for forming small accurate spheres from finely divided tungstencarbide or the like.

It has now been found that the desired balls can be produced bydistributing throughout a first inert liquid medium the finely dividedsolid material, and a second insoluble liquid having an afiinity for thepowdered material, as discrete particles, and subjecting the resultingthree-phase system to an irregular prolonged shaking action more fullydefined below. The halls produced are separated from the first liquidmedium and subjected to surface finishing, sintering or polishing asrequired. More specifically, the process of the invention comprises thefollowing steps:

(1) Preparing a dispersion in a first inert liquid medium of thepowdered solid material and a second insoluble liquid having an affinityfor the solid material, in a container having rounded inner surfaces.The manner of dispersing the second liquid is important and is describedin detail below.

(2) subjecting the resulting three-phase system to a dfifi fidd PatentedFeb. 6, 1968 shaking action to agglomerate the solid material with thesecond liquid and to cause the agglomerates to undergo a continuedimpact and ricocheting action against the container surfaces and againsteach other. The nature of this shaking and impact action, and thecontainer shape and size, are important and are discussed below.

(3) Prolonging this shaking and ricoeheting action until theagglomerates are formed into the desired round balls, and

(4) Separating the balls or shaped bodies from the first liquid and,optionally, removing the second liquid from the balls, sintering orfusing and surface finishing.

Powder materials Suitable powder materials for use in the processinclude metals and refractory metal compounds such .as aluminum, copper,iron, steels, the carbides, borides, nitrides and silicides of Ti, Zr,Cr, Ta, Mo, W, and U, and metal oxides. Particularly refractorycompounds include tungsten car-bide, titanium carbide, silicon carbideand uranium carbide. Binder metals such as Fe, Co, Ni, Cu, and Ag(including mixtures and alloys thereof), may be present in smallamounts. Solid polymeric materials such as cellulose acetate,polytetrafluoroethylene, polystyrene and polymethylmethacrylate are alsosuitable. Other examples of materials which have been balled includealumina, alundum, silica, soda glass, iron oxide, chromium oxide, tinoxide and manganese dioxide. The resulting balls may be used for ballpoint pens, ball bearings, fluidized bed catalysts, various pellets suchas nuclear fuel pellets, and the like. The use of tungsten carbidecontaining small amounts of cobalt in the present process results ingood quality balls for the ball point pen industry.

The powder particles size may be varied within wide limits, butdesirably is within the range known to give good sinterability, e.g.,from 0.1 to 100 microns. The powder is added in amounts less than about35% by volume of first liquid-and to give a fluid system. The powder maybe coated with materials such as waxes which may be retained, or areremoved prior to or during the balling process of the present invention.The coating may serve as a temporary protective coating which preventspremature p-oor ball formation (before proper dispersion is achieved),e.g., Wax coating on tungsten carbide is substantially removed bysolvent action of first liquid. A small quantity of residual wax on thesurface of the balls helps to prevent adhesion of the balls whiledrying. The condition of the powder surface may affect the size of theballs formed.

Size of balls The size of the balls is dependent on several factors,particularly the volume of second liquid: for many systerns the size ofthe balls obtained decreases from large sizes through a minimum smallersize and increases to larger sizes again as the volume of second liquidincreases, until finally a pasty mass is obtained. More violent shakingand higher temperatures usually lead to smaller sized balls.

First liquid The first liquid should be substantially inert with respectto both the powdered material and the second liquid, and of sufficientlylow viscosity at the temperature of operation so as to give afree-flowing system. The first liquid should be present in majorproportion (by volume) of the three-phase system, i.e. should be thecontinuous phase. This liquid may be a single compound or a mutuallysoluble mixture. Where the first liquid and the powder are heavier thanthe second liquid, pre- Suitable first liquids include halogenatedaliphatic or aromatic hydrocarbons, aliphatic hydrocarbons such asVarsol, aromatic hydrocarbons, liquid silicone fluids, water andsingle-phase mixtures thereof. Examples are chlorobenzene, carbontetrachloride, perchloroethylene, Varsol, heptane, benzene, toluene,xylene, and a light petroleum oil.

The viscosity of the continuous-phase liquid can be controlled by usinga solution of mutually soluble liquids of widely different viscositiesor by changing the temperature of operation.

Second liquid The second insoluble liquid may be aqueous (or a highlypolar insoluble organic material) when the first liquid is awater-insoluble organic material; or may be a water-insoluble organicmaterial when the first liquid is aqueous. This second liquid shouldhave an affinity for the powdered material (i.e. should form a dispersephase including the powdered material, within the first liquid). Forgood ball formation a larger interfacial surface tension between thefirst and second liquids should exist. Preferably the second liquid hasa wetting or solvation action on the powder. The second liquid shouldnot wet or be adsorbed by the vessel walls in the presence of the firstliquid. It is possible to treat the vessel surface to minimizeadsorption of second liquid. It may be desira=ble that this secondliquid not readily evaporate from the balls-giving balls more resistanceto handling and attrition. Examples of the second liquid are water,nitrobenzene, benzaldehyde, and water-alcohol mixtures. Water or aqueousliquids are particularly suitable due to high surface tension.

The proportions of the second liquid may range from about 3 to about250% by volume of the solid, preferably 50 to 150%. The desired amountof second liquid is influenced by the bulk volume of the powder-theamount decreases with increasing particle size of powder. The secondliquid is desirably not added to the vessel until after the walls havebeen wetted by the first liquid. Allowance should be made in the amountof second liquid for adsorption (as by container walls) or solubility inthe continuous phase. The amount of second liquid has an affect on theball size; (the size first decreases and then generally increases withincreasing amounts of second liquid until ball formation breaks down).For example, with water as second liquid, a minimum ball size oftungsten carbide has been observed to occur within the preferred range0.045 to 0.065 ml. water per gm. tungsten carbide.

The second liquid-particle surface affinity may be increased if desiredby adding surface-active compounds soluble in the second liquid but notin the first. (See Examples 18 and 19.) When the first liquid isaqueous, fatty acids may serve as the surface-active compounds.

Dispensing second liquid and powder It is important that the secondliquid become dispersed throughout the continuous phase. It is alsoimportant that the powder be dispersed through the first liquid. If thisdispersion is not obtained, the ball size is quite difficult to controland the size distribution becomes very wide.

The following techniques have been found operative for obtaining thedispersion of solid, second liquid or both:

(a) adding the second liquid as frozen particles, then mixing withwarming to release the second liquid during agitation,

(b) freezing the second liquid in situ (before any dispersion) thenmixing with warming, to release the second liquid under agitation,

(c) preparing an emulsion of the second liquid in the first in situ,e.g. (i) by adding a liquid dispersing aid (which has some solubility inboth first and second liquids) and mixing; (ii) adding the second liquidthrough an atomizing nozzle and dispersing through the first liquid; and(iii) adding the second liquid as a preformed emulsion in part of thefirst liquid,

(d) providing the powder with a temporary protective coating andremoving this coating under agitation in the three-phase system, and

(e) wetting the powder with the second liquid and then dispersing thewetted powder throughout the first liquid by severe agitation (seeExample 5). Combinations of these techniques may be used.

Ultrasonic vibration has been found to be an efiicientdispersion-forming technique. Where a preliminary emulsion is not formedthe desired dispersed agglomeration may be satisfactorily achieved ifthe powder and the first liquid are heavier than the second liquid. WithCCl WC and water, the three-phases can be kept quite separate untilagitation begins.

The amount of the liquid dispersing aid added is not critical and mayrange up to about 150% by volume of the second liquid. Suitable liquiddispersing aids (where water is the second liquid) include low molecularweight C C alcohols, particularly the propyl alcohols.

Techniques (a) and (b) above have been found to give the narrowest ballsize distribution, and may be carried out in the presence of the powder.By simply adding the three-phases to each other and subjecting to ashaking action satisfactory balls were not obtained except where theshaking was severe and prolonged enough to actually form the requireddispersed agglomerates and then controlled to give a ricochet action tothe agglomerates (see Examples -9, 36 and 37).

Container The container should have rounded inner surfaces with no sharpcorners and no confined zones where the powder can collect. Satisfactoryballs can be obtained by using containers of regular shapes such ascylinders, spheres or cones and causing them to be shaken in a complexS-dimensional pattern such as that produced by the Pica Blender-Mill(Pitchford Scientific Instruments Co. of Pittsburgh). Alternatively thecontainer may be shaken in a regular reciprocating motion, but with thecontainer having irregular dimensions such as cylinders withhemispherical ends, dimples, bends or throats; conical vessels withhemispherical ends; ellipsoidal vessels; U-tubes or various combinationsor modifications thereof. Regular cylinders or cones shaken at an angleto their axis or lying on their sides and shaken vertically, have givensatisfactory results.

The containers should not be completely filled in order to allowtranslational motion of the entire three-phase system and increasedimpact velocity. Good results have been obtained with the containerfilled with first liquid to from about 20 to about by volume (seeExamples 25 and 35). The container walls or inner surfaces should beformed from materials which are substantially chemically inert to thethree-phase system (especially to the second liquid). As mentionedabove, desirably the inner surfaces are wetted by the first liquid morereadily than by the second. If necessary the surfaces may be pretreatedto saturate their adsorptive capacity for the second liquid. Otherwisethe amount of second liquid acting on the solid particles cannot becontrolled accurately. Containers constructed from or coated withpolytetrafluoroethylene (Teflon) have been found particularly suitablewhen the second liquid is aqueous.

Shaking action Experiments have shown that good sphericity could only beobtained by vigorous shaking which imparted both: (a) translationalmotion of sufiicient velocity to cause slight deformation of theagglomerates on impact with the container surfaces, and (b) rotationalmotion to ensure that the point of impact varied each time. In otherwords, the agglomerates should undergo a continued ricocheting actionstriking the container walls at angles less than 90. Suitabletranslational motion can be achieved for example by a reciprocatingmotion of a frequency above about 60 cycles per minute. Athreedimensional shaking pattern is preferred with cylindricalcontainers as it is believed the agglomerates or balls then undergo acontinuous ricocheting action. The container geometry should be matchedto the pattern and frequency of shaking action so as to cause theagglomerates or balls to undergo a continuous ricocheting action (orachieve a type of resonance for each system).

Increasing the severity or time of shaking will usually increase thedensity of the resulting balls toward the theoretical limit (and mayalso decrease the size). This gives increased green strength. The timeof shaking may range from several minutes to several hours. Prolongingthe shaking generally results in improved sphericity. Too severe shakingmay result in rough or abraded ball surfaces. In addition to control ofthe frequency, amplitude or pattern of shaking, and the shape of thecontainer, the severity of the shaking can be further controlled byvarying the viscosity of the continuous phase liquid. Proper balancingof these various factors enables a close control to be maintained overthe balls produced.

It has been found that balls can be grown from seedor the size,sphericity or smoothness can be increased by subjecting small seed ballsto a coating treatment according to the process of the presentinvention. Smoothing agents such as waxes may be added to give a smoothsurface layer. Layers of one or several materials can be formed overballs of a different material. One or more of the core materials can beamenable to removal through the outer layer; for instance, by leaching,sublimation or decomposition. It is possible, for example, to growspheres of tungsten carbide about see-d particles of a leachable salt(e.g. sodium chloride) using as the second liquid saturated brine, andthen dissolving out the core before sintering. By agglomerating amixture containing a finely divided removable material, it is possibleto vary the porosity of the resulting balls through a wide range.

The balls of metallic, refractory or other sinterable materials may besintered according to standard techniques. The polymeric materials maybe fused by using a solvent or plasticizer as second liquid.

Ellipsoidal balls have been produced by imparting a rolling-actioncomponent to the shaking (and generally using slower shaking than forspheres). The formation of elliptical bodies is illustrated in Example27.

The balls after formation may be readily separated from the continuousphase liquid by decanting, filtering, or screening. If the sizedistribution is wide, a sizing or screening step is usually desirable. Asatisfactory size distribution for preparing balls for ballpoint pens iswith in -8+16 U.S. screen or preferably about 0.050 inch (1.3 min). Withproper control, this size can be obtained directly from the processwithout recycling. Where the balls are to be used as ball bearings, penpoints, etc. it is necessary to sinter them, for instance at 1100 C. to1500 C. for refractory carbides. A final polishing or surface finishingmay be carried out to give the desired smoothness or texture to thesurface.

The following examples illustrate the invention. Unless otherwise noteda Pica Blender'Mill was used, the shaking being carried out in a 35 ml.steel vial. Cobalt (6%) was present as a binder metal in the tungstencarbide. In some examples the tungsten carbide particles used werecoated with a small amount of paratfin wax. (Water served as the secondliquid in Examples 9 to 17 and 20 to 23 and as the first liquid inExamples 18 and 19.) In Examples 18 and 19 the unwaxed tungsten carbidesurface was treated with small amounts of fatty acids to increase theparticle surface-second liquid aifinity. Examples 5 to 13, 18 and 19were carried out at room temperature and in examples where the water wasfrozen in situ the container temperature was usually above roomtemperature after the shaking due to frictional heat.

Example 1 Example 2 About 6 g. of tungsten carbide in 14 ml. of Varsolwere cooled over Dry Ice and 0.38 ml. of water was added. After thewater was frozen, the slurry was shaken for 15 minutes. Sphericalagglomerates of the order of 1.5 mm. diameter were obtained.

Example 3 The same procedure as in Example 2 was followed, except that14 ml. of CCl were used instead of Varsol and with 0.4 ml. of waterbeing added in the form of ice. Spheres within the range of 0.6 to 1 mm.diameter were obtained. Carbon tetrachloride gives a more fluid systemthan Varsol.

Example 4 A mixture consisting of 6 g. of tungsten carbide (waxed) in 9ml. Varsol and 3 ml. CCl was cooled over Dry Ice and 0.395 ml. of waterwas frozen on the surface of the liquid. The contents were shaken for 15minutes with warming. The spheres were slightly enlarged and smoothenedby shaking the system for 8 minutes with an additional 1 g. quantity oftungsten carbide. The size distribution of the final spheres was asfollows:

Diameter mm: No., percent A variety of containers of irregulardimensions have been employed for the agglomeration of tungsten carbide.In Examples 5 to 8 the suspensions were shaken in a horizontalreciprocating motion having a displacement of 6 cm. and a frequency offrom 1 to 4 cycles per sec ond as noted.

Example 5 This invention was carried out in two 50 ml. round flasksjoined at the necks, overall length 14 cm., the neck being 1.8 cm.diameter (shaken on the long axis). Nine grams of tungsten carbide wasadded to a mixture of 20 ml. CCL; and 20 ml. Varsol. The mixture wasshaken for 1 hour at 4 cycles per second in order to disperse the solidparticles, then 0.2 ml. of water added as a fine spray with a syringe.After this suspension was shaken for 1.5 hours, a dispersion with somespherical agglomerates appeared. Another 0.1 ml. of water was added andsubstantially all suspended particles were agglomerated into spheres byshaking again for 1 hour.

Minor rough spots on the spheres were abraded off by agitation for 1hour at 1-2 cycles per second in the presence of 0.002 ml. methylalcohol added to the system. Smooth spheres of the order of 1 to 2 mm.diameter were obtained by this latter method. The technique of thisexample is not a preferred one, though operative, due to prolongedshaking required and wide size distribution obtainecl.

Example 6 This example was carried out in an ellipsoidal vessel of majoraxis 8 cm. and minor axis 5 cm. shaken along 7 the major axis. Six gramsof tungsten carbide was added to 12 ml. of CCli, and 12 ml. Varsol.While the mixture was being dispersed by ultrasonic irradiation (from a40 kc. ultrasonic generator), 0.3 ml. of water was added quickly in afine spray from a syringe. The system Was then shaken at about 1 to 2cycles per second for about 3 hours. Accurate spheres of diameter from 1to 1.5 mm. were obtained.

Example 7 This example was carried out in a glass elbow, the arms being8.5 cm. long and diameter 2.5 cm. with the ends sealed with stoppers.Six grams of tungsten carbide was thoroughly mixed and wetted with 0.3ml. water in a mortar and pesue'rhe moistened powder was added'to thevessel containing an emulsion consisting of 6 ml. Varsol, 6 ml. CCL; and0.1 ml. water prepared by ultrasonic irradiation for 3 minutes. Theslurry was shaken with the arms of the elbow upright and at an angle of45 to the direction of motion. After about 9 minutes of fast shaking (4cycles per second) somewhat unsymmetrical spherical agglomerates wereobtained. After about 1 to 2 hours of gentler shaking (l to 2 cycles persecond) spheres of the following size distribution were obtained:

Diameter mm.: No., percent The following example illustrates the use ofa copper vessel in the form of a U-tube for agglomerating finely dividedtungsten carbide to symmetrical spherical masses. This copper U-tube wasabout 17.5 cm. long and 1.8 cm. in diameter and shaken upright andaligned in the plane of the direction of motion. Six grams of tungstencarbide (waxed) were added to an emulsion of ml. toluene (previouslysaturated with water) and 0.35 ml. of water, which was prepared byultrasonic irradiation for about 3 minutes. The suspension in the U-tubewas shaken at about 4 cycles per second for about 9 minutes after whichsomewhat rough agglomerates were obtained. The system was further shakenat a slower rate (1 to 2 cycles per second) for about 1.5 hours andsmooth spheres having the following size distribution were obtained:

Diameter mm.: No., percent The spherical masses obtained could berendered very smooth on the surface by removing some of the liquid andthe suspension shaken at a slower rate. Sphere formation occurs soonerwhen the U-tube is tilted at approximately an angle of to the directionof shaking.

The following vessels also gave satisfactory results in similarexperiments:

(a) Twentyive ml. round flask, closed and rounded off at the neck;overall length about 10 cm., the neck being about 1.8 cm. diameter;shaken on its side.

(b) Double elliptical shaped vessels, about 9 cm. long and 3 cm.diameter, joined and shaken on the long axis.

(c) Round bottom flask, having two sides flattened out about 3.5 cm.wide, diameter 5.5 cm. with dimples in these sides to give aconstriction, and shaken upright. Without the dimples poor results wereobtained.

(d) Truncated conical vessels with outwardly dished ends shaken alongshort axis.

(e) Cylinders with outwardly dished ends shaken along the short axis.

In vessels of type (b) and that used of Example 5, if the joining neckis too long or too constricted poor results are obtained. Regularspheres and axially mounted cylinders shaken with a straightreciprocating rnotion gave poor results. The procedures of Examples 5 to8 are not preferred, though operative.

In the following Examples 9 to 13 satisfactory dispersion was obtained,but with rather prolonged shaking,

r preliminary emulsion formation, or wet grinding required.

Examples 14 to 17 show the sphere size distribution for various powderloadings. Examples 14 to 17 and 20 to 23 illustrate the freezing of thesecond liquid, Examples 20 to 23 use different powders, and Examples 18and 19 illustrate the use of organic second liquids. In Examples 9 to 26the shaking was in a Pica Blender-Mill.

Example Diameter of N 0. Ingredients Amounts Shaking Time SpheresRemarks Produced 9 Tungsten Carbide (unwaXedL- N0 initial dispersion oiwater but using C014 prolonged shaking.

Satisfactory balls.

Emulsion prepared by ultrasonic irradiation for 3 minutes.

Good spheres.

emulsion) Same procedure as Ex. 10. Further 0.2 ml.

water added alter 16 min. shaking.

N0 spheres"...

2-3 mm Good spheres.

Same procedure as Ex. 10.

13.2 mm Good spheres.

13 Tungsten Carbide (unwaxed) Water Dispersed in- CCl.; 71x11 Varsol 7ml 6g 0.35 ml llungsteu carbide and water premixed by grinding to wcttedsolid powder.

Satisfactory balls.

1 Emulsion.

Example N 0.

Ingredients Amounts Shaking Time Sphere Size DistributionUS ScreenRemarks 8+10 l+14 12+14 14+16 14 Tungsten Carbide 20 g CarbonTetrachloride Tungsten Carbide. Carbon Tetrachlo Water* Tungsten Carbide C arbon Tetrachloride W ater z Good spheres.

Good spheres.

Good spheres.

Good spheres.

Water frozen in situ in 35 m1. steel container in Dry Ice bath. Thelimit to loading in this container is about 50 gm. of tungsten carbideas the losses (or unballed or caked material) become significant (aboutwt.). At a loading of about large bails. Example represents a desirablesize distribution for balls for ball point pens.

Example N0.

Ingredients Amounts Shaking Time Diameter of Spheres Produced RemarksNitrobenze Oleie Acid Benzaldehyde Tall oil acids Silicon carbide (-400mesh) C 014 Mixture prepared in situ.

Good spheres.

Mixture prepared in situ.

Good spheres.

Good spheres. Narrow size distribution.

0.2-0.5 mm Good spheres.

Water 1 Good spheres.

23 Titanium Carbide Good spheres.

1 Water frozen in a 25 ml. stainless steel vial. The C014 (or firstliquid) was added followed by the powder.

Stainless steel vial capacity about ml 25 Unwaxed tungsten carbidepowder gm 20 Example 24 Water (frozen in situ) ml 1 Paraifin wax (as acoating agent) gm 0.3 Gem grade alumina (0.1 microns) "gr m" 1 Carbontetrachloride ml 22 ml 1.1 Water When these materials (about 95% vialcapacity) n-Propyl alcohol ml 0.2

were agitated for 12 rnlnutes, mlxtures consisting of Paraffin Wax irrcular lli ti a1 and ll f t' of s h r'cal Carbon tetrachloride ml 10 g e pC a Sma raclon p 51 Example 25 In general, desirable spherical bodieswere obtained when the vessels were filied with first liquid to fromabout 20 to about 80% by volume. Undesirable agglomcrates were obtainedwhen the vessels were filled to nearly full capacity as illustrated.

bodies were obtained. The spherical masses were of the order of 0.2 to0.5 mm. in diameter. Decreasing the volume of CCL; to below about 18 ml.gave satisfactory results.

Example 26 The following example illustrates nearly maximum amounts oftungsten carbide powder which can be employed with the same vessel (25ml. capacity) whereby very desirable spherical bodies were obtained.

Unwaxcd tungsten carbide grn 40 Water (frozen in situ) ml 2.1 Carbontetrachloride ml 12 After agitating the system for 12 minutes about 97%of the original powdered material was in the form of spherical bodies ofthe order to l to 2 mm. in diameter. However, unsatisfactoryagglomerated bodies were obtained when the amount of tungsten carbidepowder 50 gm. oi tungsten carbide the size distribution gives more 1 1was increased to 50 grams (solid volume increased about 1 cc.) e.g.

Unwaxed tungsten carbide powder gm. (-1 cc.) 50 Water (frozen in situ)ml 2.6 Carbon tetrachloride ml 12 This system was agitated for 12minutes and a small quantity of agglomerated material of poor sphericityand large amounts of caked tungsten carbide were obtained.

Example 27 example in which elliptical bodies were formed.

Wax coated carbide powder gm 20 Water ml 1.0 n-Propyl alcohol "ml" 0.2Carbon tetrachloride ml 11 The ingredients were added to the conicalvessel described above in the following order: carbon tetrachloride,metaliic powder, n-propyl alcohol and water. The vessel was then shakenfor 15 minutes at 2 cycles per second with the short axis in thedirection of motion. Elliptical bodies having substantially major axis/minor axis ratios of about -1.4 to 1.7 were obtained. When the vesselwas agitated with the long axis in the direction of motion, sphericalmasses varying from 1 to 2.5 mm. diameter were obtained.

Another similar suspension was agitated at an angle less than 90 to thedirection of motion and very desirable spherical bodies varying from 1.5to 3.0 mm. in diameter were obtained.

Example 28 The following example is given to illustrate the minimumamounts of second liquid giving satisfactory results.

These ingredients were shaken in the conical vessel described in Example27 by a horizontal reciprocating action for 15 minutes, at an angle lessthan 90 to the direction of motion. Undesirable rough unsymmetricalagglomerates were obtained.

(b) When the amount of water was increased to 1.0 ml. very desirablespherical agglomerated bodies were obtained.

(c) Very desirable spherical masses were also obtained when the amountof carbon tetrachloride was increased to 22 ml., n-propyl alcoholincreased to 0.3 ml. and water held constant at 1.0 ml.

These and other experiments confirm that the amount of first liquid canbe varied over a wide range (within 2090% of vessel capacity) and stillspherical agglomerates can be obtained.

Example 29 This example illustrates the minimum quantity of npropylalcohol required as dispersing aid.

12 were agitated in the conical vessel of Ex. 27 at an angle less than90 to the direction of motion (horizontal) for 15 minutes. The resultsobtained are summarized below:

Vol. of n- Percent Propyl alcohol Appearance of Size Range Alcohol,Based on Agglornerates (diam.)

ml. Water 0 Large bodies of poor 2-5 mm. crosssphericity. section. 0.055 Large smoother bodies of 2.5 to 4.5 mm.

poor sphericity. cross-section. 0 1 l0 Mixture of poor and good 2 to 3mm. spherical bodies. 0.2 20 Good spherical bodies 1 to 2.5 mm. 0. 4 40(lo 1.3 to 2.5 mm. 0. 6 0.9 to 2 mm. 0.8 0.9 to 2.5 mm. 1.0 0.8 to 2.0mm. 1. 4 0.7 to 1.9 mm.

In this system at least about 15% of n-propyl alcohol (based on water)should be used to obtain good distribution of the water and goodspheres.

The following apparatus was used to obtain spheres on a larger scale. Acontainer was fastened to an arm which was pivoted at one end and freeto oscillate at the other end. The free end was oscillated at 450 cyclesper minute in the horizontal plane. The following shapes of containerswere fastened on the arm near the free end and were found to be verysatisfactory: (a) ellipsoid, (b) cylinder with hemispherical ends, and(c) a truncated cone with hemispherical base. (Elbowand conical-shapedcontainers and straight cylinders were found to be unsatisfactory withthis shaking action.) Both containers (a) and (b) were shaken at rightangles to their long axis. Container (c) was shaken with the base of thecone pointing away from the pivoted end of the arm. Container (c)constructed of polytetrafluoroethylene with a capacity of ml. was usedin the following examples. Shaking time was 5-7 minutes and shakingstroke 4 inches (of arc).

Example 30 200 grams of waxed tungsten carbide powder suitable forsintering was dispersed in 40 ml. of carbon tetrachloride. The mixturewas shaken with 10.2 ml. of water and spheres of'about 0.13 mm. diameterwere formed. A second batch of waxed powder using a similar formulationand procedure resulted in spheres of 3.9 mm. diameter. However, when thewater was modified with 1 ml. of npropyl alcohol similar spheres of theorder of 0.13 mm. diameter were consistently obtained. The size ofspheres and the ease of sphere formation in this system variesconsiderably with the properties of the tungsten carbide powder, e.g.particle size and shape, and whether the surface is waxed or unwaxed.The degree of dispersion of the Water also has a marked effect. Apparentapproximate upper and lower concentration limits for water as the secondliquid giving good spheres in this system with tungsten carbide are from0.045 to 0.065 ml. of water per gram tungsten carbide.

Example 31 n-Propyl alcohol when added to water (second liquid) has beenfound to exert a profound effect on the size of the balls formed.Similar results were obtained with both waxed and unwaxed powders andthis addition offers a way of controlling sphere size by which some ofthe variability in powder properties can be overcome. 100' grams ofwaxed tungsten carbide was added to 40 ml. of carbon tetrachloridefollowed by 5.3 ml. of water with the following additions of n-propylalcoholn-Propyl alcohol, ml.: Sphere diameter, mm.

Example 32 Unwaxed tungsten carbide powder 100 gl11S., carbontetrachloride 40 ml., water 5.3 ml., and n-propyl alcohol 1.2 ml. weremixed and shaken as in Ex. 30. Spheres of the order of 1.3 mm. diameterwere readily formed.

Example 33 Waxed tungsten carbide 100 grams, carbon tetrachloride 15 mL,toluene 15 ml., water 5.0 ml., and n-propyl alcohol 1.6 ml. were mixedand shaken as in Ex. 30. Smooth spheres were formed of diameter 1.3 to1.5 mm.

Example 34 Waxed tungsten carbide 100 grams, perchloroethylene 40 ml.,water 5.0 ml. and n-propyl alcohol 1.5 ml. were mixed and shaken as inEx. 30. Satisfactory spheres of the order of 1.3 mm. diameter wereformed.

Example 35 The amount of loading has been found to affect the uniformityof the spheres produced. The spread in sphere sizes has been found to bemarkedly greater when 10 gram batches of tungsten carbide were balled(in 40 ml. carbon tetrachloride) than when 100 gram batches were balled.Successful results have been obtained with batches of up to 200 grams inthe 150 ml. container (c) above. Increasing the amount of powder tobeyond 200 grams resulted in decreased effectiveness.

The amount of first liquid has been varied widely and again no criticallimits have been found-except that the powder must be dispersed in it togive a fluid system (lower limit)while using excessive amounts of firstliquid becomes inefiicient. Also the effectiveness of the shaking actionis decreased if greater than about 80% of the volume of the vessel isfilled. [Using more than 100 ml. of first liquid in a 150 ml. vesselgave balls of larger size and poorer sphericity than when less than 100ml. was usedindicating that dispersion of second liquid becomes poor inhighly filled vessels] The speed of shakin in the pivoting arm apparatushas been varied over the range 100 to 560 cycles per minute. Resultsindicate that at low speeds non-sphericity and non-uniformity of sizeare increased. Generally shaking at above about 300 c.p.m. gave goodspheres.

It will be seen from the examples that many variations may be made inthe pattern, time and speed of shaking and in the containershape-providing that proper dispersion of the second liquid is obtainedand that a resonance or continuing ricochet action of agglomerates issustained.

The following two examples illustrate the formation of spheres from twofurther non-metallic powders, and the use of a second liquid containinga small amount of a binder for increased green strength of the spheres.A piv oted arm reciprocating shaker [similar to Example 30, but usingthe container (b)] was used. The vessel had a ca pacity of 280 cc.

Example 35 Soda glass powder g 16% sodium silicate solution cc 1.8Carbon tetrachloride ml 75 Shaking action 409 c.p.m. for 2 hours.

The materials were added to the vessel in the following order: sodaglass, carbon tetrachloride and sodium silicate solution. Good spheresof a size ranging from 3 to 4 mm. diameter were obtained.

145 Example 37 Silica (l43l microns) .g 10 16% sodium silicate solutioncc 2.6 Carbon tetrachloride ml 75 Shaking action 350 c.p.m. for 2 hours.

The materials were added to the vessel in the order silica, carbontetrachloride and sodium silicate solution. Good spheres of the order of3 to 4 mm. diameter were obtained. In both Examples 36 and 37 thespheres had good green strength and withstood handling, due to thesodium silicate present.

We claim:

1. A process for forming balls from finely divided powders in atwo-phase liquid system comprising:

(a) adding the powder and a second insoluble liquid to a first inertliquid medium, the second liquid having a preferential atfinity for thepowder,

(b) subjecting the three-phase system to a shaking action in a containerhaving rounded inner surfaces, to form dispersed agglomerates of thepowder with the second liquid and to cause the agglomerates to undergo acontinued impact and ricocheting action against the rounded surfaces,

(c) prolonging the impact and ricocheting action until the agglomeratesare formed into the desired balls, and

(d) separating the balls from the first liquid.

2. A process for forming balls from finely divided powders in atwo-phase liquid system comprising:

(a) dispersing the powder and a second liquid throughout a first inertliquid medium to give a fluid threephase system, the second liquid beinginsoluble in the first and having a preferential aflinity for thepowder,

(b) shaking the three-phase system in a container having rounded innersurfaces, the container being filled to from about 20 to vol. percentcapacity, to agglomerate the powder with the second liquid and causingthe agglomerates to undergo a continued impact and ricocheting actionagainst the rounded surfaces,

(c) prolonging an impact and ricocheting action to form the desiredballs from the agglomerates,

(d) separating the balls from the first liquid, and

(e) removing the second liquid from the balls.

3. A process for forming balls from finely divided powders in atwo-phase system comprising:

(a) dispersing the powder in amounts less than about 35% by vol. offirst liquid, and droplets of a second liquid in amounts from about 3 to250% by vol. of powder solid, throughout a first inert low viscosityliquid, the second liquid being insoluble in the first, and having ahigh surface tension and a preferential afiinity for the powder,

(b) shaking the three-phase system in a container having rounded innersurfaces, the container being filled to from about 20 to 90 vol. percentcapacity, to agglomerate the powder with the second liquid and causingthe agglomerates to undergo a continued impact and ricocheting actionagainst the rounded surfaces,

(c) prolonging impact and ricocheting action sufficiently to shape anddensify the agglomerates into the desired balls,

(d) separating the balls from the first liquid, and

(e) removing the second liquid from the balls.

4. A process for forming balls from finely divided powders in atwo-phase liquid system comprising:

(a) adding the powder to a first inert liquid in amounts less than about35% by vol., contacting with a second insoluble liquid in a frozen statein amounts from about 3 to 250% by vol. of powder solid, and dispersingwith warming to form a fluid three-phase system, the second liquidhaving a preferential affinity for the powder,

(b) shaking the three-phase system in a container having rounded innersurfaces, the container being filled to from about 20 to 90 vol. percentcapacity, to agglomerate the powder with the second liquid and causingthe agglomerates to undergo a continued impact and ricocheting actionagainst the rounded surfaces,

(c) prolonging impact and ricocheting action sufficiently to shape anddensify the agglomerates into the desired balls,

(d) separating the balls from the first liquid, and

(e) removing the second liquid from the balls.

5. A process for forming balls from finely divided powders in atwo-phaseliquid system comprising:

(a) preparing an emulsion of a second insoluble liquid in a first inertliquid and dispersing the powder throughout the first liquid, the secondliquid being present in amounts from about 3 to about 250% by vol. ofpowder solid and having preferential affinity for the powder,

(b) shaking the three-phase system in a container having rounded innersurfaces, the container being filled to from about 20 to 90 vol. percentcapacity, to agglomerate the powder with the second liquid and causingthe agglomerates to undergo a continued impact and ricocheting actionagainst the rounded surfaces,

(c) prolonging impact and ricocheting action sufficiently to shape anddensify the agglomerates into the desired balls,

(d) separating the balls from the first liquid, and

(e) removing the second liquid from the balls.

6. The process of claim 5 wherein the emulsion is prepared in situ byadding a liquid dispersing aid which has solubility in both first andsecond liquids.

7. The process of claim 6 wherein the liquid dispersing aid is a lowmolecular weight C to C alcohol.

8. The process of claim 7 wherein the alcohol is a propyl alcohol and ispresent in amounts up to about 150% by vol. of second liquid.

9. A process for forming balls from finely divided powders in atwo-phase liquid system comprising:

(a) dispersing the powder in amounts less than about 35% by vol. offirst liquid, the powder having a temporary protective coating which hassome solubility in the first liquid, and droplets of a second liquid inamounts from about 3 to 250% by vol. of powder solid, throughout a firstinert liquid, the second liquid being insoluble in the first and havingno affinity for the protective coating, but preferential affinity forthe powder,

(b) shaking the three-phase system in a container having rounded innersurfaces, the container being filled to from about 20 to 90 vol. percentcapacity to remove the temporary protective coating and to agglomeratethe powder with the second liquid, and causing the agglomerates toundergo a continued impact and ricocheting action against the roundedsurfaces,

(0) prolonging impact and ricocheting action sufficiently to shape anddensify the agglomerates into the desired balls,

(d) separating the balls from the first liquid, and

(e) removing the second liquid from the balls.

10. The process of claim 9 wherein the temporary protective coating is awax,

11. The process of claim 3 wherein the first liquid is organic and thesecond liquid is aqueous,

12. The process of claim 3 wherein from 50 to 150% of second liquid isused.

13. The process of claim 3 wherein seed balls are dispersed togetherwith the powder, the second liquid also having an affinity for the seedballs, the powder forming a coating on the seed balls.

14. The process of claim 13 wherein the seed balls are subsequentlyremoved through the outer layer of the final composite ball.

15. The process of claim 3 wherein the shaking action is controlled toimpart a rolling component to the ball path, causing the formation ofellipsoidal balls.

16. A process for forming balls from finely divided powder comprisingtungsten carbide in a two-phase liquid system comprising? (a) dispersingthe powder, droplets of water and up to 150% by vol. based on the waterof n-propyl alcohol, in a chlorinated hydrocarbon liquid, the amount ofthe powder being less than about 35% by vol. of the chlorinatedhydrocarbon and the amount of the water being from about 50 to 150% byvol. of solids,

( b) shaking the three-phase system in a container having rounded innersurfaces of polytetrafluoroethylene, the container being filled to fromabout 20 to 90 vol. percent capacity, to agglomerate the powder with thewater, and causing the agglomerates to undergo a continued impact andricochetin-g action against the rounded surfaces,

(c) prolonging impact and ricocheting action sufficiently to shape anddensity the agglomerates into the desired balls,

(d) separating the balls from the chlorinated hydrocarbon liquid,

(e) removing the water from the tungsten carbide :balls, and

(f) sintering the tungsten carbide balls.

17. A process for forming balls from finely divided powders in atwo-phase liquid system comprising:

(a) adding the powder and a second insoluble liquid to a first inertliquid medium, the second liquid having a preferential afiinity for thepowder,

(b) shaking the three-phase system in a container having rounded innersurfaces so that the contents thereof move in a path having bothtranslational and rotational components so that the powder particlesform dispersed agglomerates and the agglomerates repeatedly strike theinner surfaces of the container at angles of less than 90 and undergo acontinued impact and ricocheting action against the rounded surfaces,the shaking of the container being the sole force being applied foreffecting agitation and mixing of the three-phase system,

(c) continuing the impact and ricocheting resonance of the system untilthe agglomerates form the desired balls, and

(d) separating the balls from the first liquid.

References Cited UNITED STATES PATENTS 3,228,749 1/1966 Akimoto 264.53,264,379 8/1966 Hammer et al 264-.5 2,553,714 5/1951 Lucas -2043,303,825 2/1967 Shurnan et al. 75-204 L. DEWAYNE RUTLEDGE, PrimaryExaminer,

